Standing at the intersection of three foreign policy crises and a perennial constitutional tension, Bob Corker, R-Tenn., incoming chairman of the Foreign Relations Committee, may be the senator who matters most in 2015.

Without an authorization for use of military force (AUMF) tailored to novel circumstances, America is waging war against an entity without precedent (the Islamic State).

Iran is pursuing nuclear weapons during negotiations that should involve congressional duties.

Russia is revising European borders by force and, like Iran, is the object of a U.S. experiment testing the power of economic sanctions to modify a dictator's behavior.

As Congress weighs its foreign policy role regarding these three matters, Corker treads the contested terrain between deference to presidential primacy in foreign policy and the need for collective wisdom and shared responsibility.

Were Barack Obama more prudent than vain, he would want congressional collaborators in problematic foreign ventures. He has, however, ignored the historical norm whereby presidents specify the authority they need. He has offered no substitute for the 60-word AUMF from Sept. 18, 2001, which authorized force against "those nations, organizations, or persons" complicit in 9/11.

This was a decade before the Islamic State — which is not a nation and has no clear borders or regime with which to deal — existed.

Remember the "Khorasan group"? On Sept. 23, when announcing the beginning of airstrikes against the Islamic State, Obama cited this hitherto unmentioned menace in connection with the U.S. military action. It has hardly been mentioned since. Should an AUMF mention it?

Corker believes that congressional action legalizing Obama's current military actions would be akin to responding to a teenager who habitually drives too fast by raising the speed limit.

Nevertheless, many legislators, including some who are indignant about Obama unilaterally setting environmental and immigration policies, seem reluctant to leash him regarding war. Others want an AUMF that would place geographic and time limits on U.S. military action, and would bar use of U.S. ground troops.

Corker hopes an AUMF debate will, for the administration, lay out a plausible path to stated goals regarding Syria.

Meanwhile, the training of Syrian moderates remains as chimerical as the Bashar al-Assad regime's barrel bombs are real, and Congress continues, Corker notes disapprovingly, to fund America's wars off budget.

Making a mockery of supposed budget targets, there was another $73 billion "OCO" — overseas contingency operations — expenditure in the recent $1.1 trillion spending bill in the 14th year of an "emergency."

The Banking Committee, on which Corker sits, has jurisdiction over Iranian sanctions, and has passed new ones. Tip-toeing through a diplomatic minefield, Corker is working on ways for Congress to affect the negotiations positively without jeopardizing them.

Corker and Sen. Lindsey Graham, R-S.C., have drafted legislation requiring the president to submit to Congress, within three days, any comprehensive agreement reached with Iran, and would have Congress hold hearings on it in 15 days. Congress would have an additional 15 days to introduce a joint resolution of disapproval.

If the president does not submit any agreement, or if a resolution of disapproval is enacted, then prior sanction relief is ended. Iran might stymie this process by prolonging the negotiations until it reaches what Corker thinks Iran considers "the sweet spot": At least for now, getting to "a screwdriver turn" away from possessing a weapon, then pausing.

Regarding Russia, too, Corker and his committee are relevant to U.S. efforts at behavior modification. Vladimir Putin, says Corker, cannot be allowed to succeed in his aggression, and must pay a heavy price until he changes course. But he should not be forced to fail so calamitously that a destabilized Russia destabilizes the region.

Banking and other sanctions, coinciding with a roughly 50 percent decline in the price of oil, have convulsed this ramshackle country. In what may be a harbinger of an enlarged congressional role in foreign policy, Obama has signed legislation, co-introduced by Corker, that increases sanctions on Russia and provides $350 million in military aid to Ukraine.

Corker says he is a former builder of shopping centers, a real estate entrepreneur, and a former mayor (of Chattanooga) who had — he forms a zero with his thumb and forefinger — "this much" foreign policy experience before becoming a senator in 2007.

Never mind. He has now visited 64 countries, some of them multiple times, and his mind is unclouded by long immersion in the conventional thinking of the foreign policy clerisy, with its inclination to disparage strong congressional initiatives in foreign policy.

George F. Will is one of today's most recognized writers, with more than 450 newspapers, a Newsweek column, and his appearances as a political commentator on Fox news. Read more reports from George Will — Click Here Now.